The present invention relates to a Cu--Pb alloy bearing and, more particularly, to a Cu--Pb alloy bearing of an excellent corrosion resistance.
Regarding a bearing alloy layer of a Cu--Pb alloy used for an internal combustion engine, Pb-phase grains dispersed in the Cu matrix are readily corroded by acid. Especially in the case of lubrication oil after long-time use (hereinafter referred to as deteriorated oil), acid substances such as an organic acid (R--COOH) changed in quality corrode Pb-phase grains very easily. In order to improve the corrosion resistance, Sn and In are added to the bearing alloy. However, those elements dissolve into the Cu matrix so that the corrosion resistance of Pb-phase grains will not be improved. In this regard, there has been an attempt to substituted Bi (JP-A-4-202726) for Pb improve the corrosion resistance. However, such substitution is not sufficient because the proposed alloys are degraded in conformability and anti-seizure property. Further, in accordance with an increase of the output of an internal combustion engine in recent years, even higher fatigue resistance and higher corrosion resistance have been demanded.
In this regard, there have been known alloy bearings in which an overlay layer made of Pb--Sn, Pb--Sn--Cu or Pb--Sn--In alloy is formed on the bearing alloy layer so as to enhance not only the conformability but also the corrosion resistance. Further, among these alloy bearings including the overlays, there have been known bearings in which an intermediate Ni layer is provided between the bearing alloy layer and the overlay, whereby Sn or In in the overlay is inhibited from diffusing into the bearing alloy during heat treatment and operation of the engine so that some properties including corrosion resistance produced by the overlay will not fail to be produced. However, those of the Cu--Pb alloy bearings which do not include intermediate Ni layers have a problem that when the overlay is worn with long-time use and the bearing alloy layer is exposed, it is directly contacted with deteriorated oil and quickly becomes corroded. On the other hand, those of the Cu--Pb alloy bearings which include intermediate Ni layers have a problem that provision of the intermediate Ni layer increases the costs. Besides, when the overlay becomes worn with long-time use and the hard intermediate Ni layer is exposed, whereby seizure is caused in the internal combustion engine.